Multi-level stacked acoustic wave (aw) filter packages and related fabrication methods

ABSTRACT

A multi-level stacked AW filter package including a first acoustic wave (AW) filter stacked on a second AW filter employs semiconductor fabrication methods and structures, including a metallization layer comprising interconnects to couple a contact surface to the second AW filter. Each AW filter includes an AW filter circuit on a semiconductor substrate. A second substrate disposed on a frame on the substrate protects the AW filter circuit. In a multi-level AW filter package, the second substrate of the first AW filter comprises a glass substrate with a similar expansion rate as the semiconductor substrate. The interconnects coupling the second AW filter to the contact surface are disposed on insulators on the side wall surfaces of the semiconductor substrates of the first AW filter for isolation. In a stacked AW filter package comprising a single AW filter, the interconnects couple the contact surface to the AW filter.

BACKGROUND I. Field of the Disclosure

The field of the disclosure relates to acoustic wave (AW) filterpackages, including AW filters with AW filter circuits on substrates andstacking substrates comprising AW filter circuits.

II Background

Manufacturers of mobile wireless devices can make new devices attractiveto buyers by increasing the functional capabilities of the devices witheach new generation. Increasing the capability of a device typicallyrequires more circuitry be added, which occupies more space, but thedevice sizes of hand-held devices, for example, are based on the sizesof human hands, which remain the same. Methods for achieving an increasein function without an increase in device size include reducing thedimensions of circuits providing the functional capabilities so thatmore circuits can fit into the internal space of a device. A reductionin the area of transistors and wires can increase circuit density,making it possible to reduce a size of a semiconductor chip or to putmore circuitry on a semiconductor chip of a given size. Another methodfor increasing the number of integrated circuits (ICs) in a package isthree-dimensional (3D) IC stacking. By this method, an area previouslyoccupied by two ICs placed side-by-side may be reduced (e.g., cut inhalf) by vertically stacking one IC over another in the same horizontalarea, resulting in only a small increase in package height. The activecircuits in stacked ICs are enveloped in layers of metal, dielectricmaterials, insulators, and/or molding compounds, and stacking ICs in apackage may not significantly interfere with their operation.

Hand-held devices also include wireless devices that include radiofrequency (RF) circuits. RF circuits include analog filters that areconventionally formed as acoustic wave (AW) devices containing AW filtercircuits. Examples of AW filter circuits include surface acoustic wave(SAW) filter circuits and bulk acoustic wave (BAW) filter circuits. AnAW filter circuit converts an electrical input signal into acousticwaves in a piezoelectric material. In one example, a SAW filter circuitincludes a first interdigital transducer (IDT) on a surface ofpiezoelectric material configured to receive an RF signal and a secondIDT on the surface configured to generate a filtered RF signal. The RFsignal is converted into acoustic waves that propagate through thesurface of the piezoelectric material from the first IDT to the secondIDT. The acoustic waves in the SAW filter circuit need to be protectedfrom physical contact, which would interfere with wave propagation. Theprotection is provided by providing a cavity or air space above thesurface of the substrate. Since such cavities are necessary to protectan AW filter circuit and stacked ICs do not require such cavities, AWfilter devices have not been stacked by the conventional methods used in3D IC stacking.

SUMMARY OF THE DISCLOSURE

Exemplary aspects disclosed in the detailed description includemulti-level, stacked acoustic wave (AW) filter packages that includestructures to support stacked AW filters. Related fabrication methodsare also disclosed. Certain structures and fabrication methods disclosedherein that support a multi-level stacked AW filter package can also beemployed in an AW filter package that only includes a single AW filter.In this regard, AW filter packages disclosed herein include one or moreAW filters that each include a first substrate comprising a firstsurface (e.g. a piezoelectric material) with at least one AW filtercircuit disposed thereon. Each AW filter circuit comprises first andsecond interdigital transducers (IDTs) to provide radio frequency (RF)signal filtering. Each AW filter also includes a frame coupled to thefirst substrate and surrounding the at least one AW filter circuit. Asecond substrate (e.g., a cap substrate) disposed on the frame enclosesan air cavity inside the frame between the first substrate and thesecond substrate. In one exemplary aspect, the AW filter packageincludes a multi-level AW filter package that includes multiple AWfilters stacked in a vertical direction in a stacked arrangement toinclude multiple filter circuits to filter multiple frequencies orfrequency bands. The multi-level AW filter package includes a first, topAW filter, including at least a first AW filter circuit disposed on afirst substrate, and a second substrate disposed on a first framedisposed on the first substrate. The first substrate disposed on asecond frame disposed on a third substrate encloses a second, bottom AWfilter including at least a second AW filter circuit to form themulti-level AW filter package. The first substrate and the thirdsubstrate can be formed from a semiconductor material as semiconductorsubstrates. Fabricating the first substrate and the third substrate assemiconductor substrates can allow the AW filter package to befabricated using semiconductor fabrication processes and techniques usedin fabricating semiconductor die packages.

In a first exemplary aspect of a multi-level AW filter package, metalinterconnects provided for the first AW filter are separate from metalinterconnects provided for the second AW filters to provide separatesignal paths for receiving RF signals in the respective AW filtercircuits from contact pads on a contact surface of the second substrateand providing respective filtered RF signals to the contact pads on thecontact surface. In this regard, first metal interconnects in the formof metalized vertical interconnect accesses (vias) are disposed throughthe second substrate to a surface of the first substrate to provideinterconnect paths for the first, top AW filter. Further, metallizationlayers that include second metal interconnects are formed on the outerperimeter walls of the stacked AW filters to provide interconnect pathsfor the AW filter circuits of the second, bottom AW filter that arephysically and electrically separated from the interconnect paths of thefirst, top AW filter. The second metal interconnects of themetallization layers provide interconnect paths between the second,bottom AW filter circuit and first contact pads on the contact surfaceof the second substrate of the first, top AW filter. Forming theinterconnect paths of an AW filter in an AW filter package as metalinterconnects in metallization layers, such as redistribution layers(RDLs) for example, allows metallization layer fabrication processes(e.g., RDL, fabrication processes) to be employed to fabricate the AWfilter package. Metal interconnects in metallization layers can beemployed to provide metal interconnects for interconnect paths of an AWfilter, even in an AW filter package that only includes a single AWfilter and does not include stacked AW filters. Also, in the example ofAW filter packages, side wall surfaces of the second substrate, thefirst substrate, and the third substrate can be staggered in ahorizontal direction to support the formation of the metallizationlayers on the outer perimeter walls of the stacked AW filters to providethe interconnect paths from the contact pads on the contact surface ofthe second substrate to the second, bottom AW filter circuit. Thestaggered side wall surfaces create shoulder areas on the firstsubstrate that extend out from the second substrate and, in themulti-level AW filter package, create lower shoulder areas on the thirdsubstrate that extend out from the first substrate of the AW filterpackage. The staggered side wall surfaces provide support for theformation of the metal interconnects on the outer perimeter walls of thestacked AW filters and avoid overlaps that create “negative exposure”areas where the metal interconnects may not be able to be formed.

In another exemplary aspect of a multi-level AW filter package, metalinterconnects (e.g.,. RDL interconnects) are formed on the outerperimeter walls of the stacked AW filters to provide an interconnectpath from the contact surface of the second substrate to the second,bottom AW filter that necessarily extends onto the outer walls of thefirst substrate of the first, top AW filter before extending down to thethird substrate of the second, bottom AW filter. The first substrate ofthe first, top AW filter is disposed between the second substrate andthe third substrate of the second, bottom AW filter. Thus, electricalsignals carried in the second metal interconnects in the interconnectpath from the contact pads on the second substrate down to the thirdsubstrate of the second AW filter may come into electrical contact withthe first substrate of the first, top AW filter, causing a leakagecurrent path between the second metal interconnects and the at least oneAW filter circuit of the first, top AW filter. A leakage current mayinterfere with the performance of AW filter circuits on the firstsubstrate and the third substrate. In this regard, in another exemplaryaspect, one or more insulating layers are disposed on the outerperimeter walls of the stacked AW filters between the first substrateand the second metal interconnects. The second metal interconnects areformed over the one or more insulating layers disposed on the outerperimeter walls of the stacked AW filters. In this manner, theelectrical signals carried by the second metal interconnects areisolated and insulated from the first substrate of the first, top AWfilter.

In another exemplary aspect of an AW filter package, the secondsubstrate of the first, top AW filter can be made of a glass materialthat can be laser processed to allow precise openings to be formed inthe second substrate to form the metalized vias for the first metalinterconnects to the first AW filter circuit. A glass second substratemay also advantageously provide mechanical robustness and stability tothe AW filter package. The Coefficient of Thermal Expansion (CTE) ofglass is higher than the CTE of a polymer material that hasconventionally been used to form a second substrate, for example.Especially for stacked, multi-level AW filter packages where multiple AWfilter cavities are formed on each substrate in a stacked arrangement,it is important to provide mechanical stability to the AW filter packageto avoid any fracture of the second substrate or first substrate due todeflection in the filter cavities. Also, using a glass second substratecan provide mechanical stability for substrates of reduced thicknessthat are employed to keep the overall height of the AW filter packagewithin a desired height budget.

In one exemplary aspect, a stacked AW filter package is disclosed. Thestacked AW filter package comprises a first substrate comprising a firstsurface; an AW filter circuit on the first surface of the firstsubstrate; a frame disposed on the first surface of the first substrate;a second substrate comprising a contact surface and a side wall surface,the second substrate disposed on the frame to form a cavity between theAW filter circuit and the second substrate; and a metallization layercomprising at least one metal interconnect coupled to the contactsurface of the second substrate and the first surface of the firstsubstrate, the at least one metal interconnect disposed on the side wallsurface of the second substrate.

In another exemplary aspect, a method of fabricating a stacked AW filterpackage is disclosed. The method comprises firming a first substratecomprising a first surface; forming an AW filter circuit on the firstsurface of the first substrate; forming a frame on the first surface ofthe first substrate; forming a second substrate comprising a contactsurface and a side wall surface; disposing the second substrate on theframe to form a cavity between the AW filter circuit and the secondsubstrate; and forming a metallization layer comprising at least onemetal interconnect coupled to the contact surface of the secondsubstrate and the first surface of the first substrate, the at least onemetal interconnect disposed on the side wall surface of the secondsubstrate.

In another exemplary aspect, a stacked AW filter package is disclosed.The stacked AW filter package comprises a first substrate comprising afirst surface and a side wall surface; a first AW filter circuit on thefirst surface of the first substrate; a first frame disposed on thefirst surface of the first substrate; a second substrate comprising acontact surface and a side wall surface, the second substrate stacked onthe first frame to form a cavity between the first AW filter circuit andthe second substrate; a third substrate comprising a second AW filtercircuit on a second surface of the third substrate; a second framedisposed on the second surface of the third substrate; the firstsubstrate disposed on the second frame to form a second cavity betweenthe second AW filter circuit and the first substrate; a metallizationlayer comprising at least one metal interconnect coupled to the contactsurface of the second substrate and the second surface of the thirdsubstrate, the at least one metal interconnect disposed on the side wallsurface of the first substrate; and an insulator disposed on the sidewall surface of the first substrate between the side wall surface of thefirst substrate and the at least one metal interconnect.

In another exemplary aspect, a method of fabricating a stacked AW filterpackage is disclosed. The method comprises forming a first substratecomprising a first surface and a side wall surface; forming a first AWfilter circuit on the first surface of the first substrate; forming afirst frame on the first surface of the first substrate; forming asecond substrate comprising a contact surface and a side wall surface;disposing the second substrate on the first frame to form a first cavitybetween the first AW filter circuit and the second substrate; forming athird substrate comprising a second AW filter circuit on a secondsurface of the third substrate; forming a second frame on the secondsurface of the third substrate; disposing the first substrate on thesecond frame to form a second cavity between the second AW filtercircuit and the first substrate; forming an insulator on the side wallsurface of the first substrate; and forming a metallization. layercomprising at least one metal interconnect coupled to the contactsurface of the second substrate and the second surface of the thirdsubstrate, the at least one metal interconnect disposed on the insulatoron the side wall surface of the first substrate.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an illustration of one example of a surface acoustic wave(SAW) device that may be employed in stacked acoustic wave (AW) filterpackages;

FIGS. 2A-2C are cross-sectional side views of a multi-level stacked AWfilter package including a first substrate of a first, top AW filter, asecond substrate stacked on the first substrate, the first substratestacked on a third substrate of a second, bottom AW filter, and a metalinterconnect in a metallization layer on the outer perimeter walls ofthe stacked AW filters coupling the second, bottom AW filter to contactpads on the second substrate;

FIG. 3 is an illustration of an AW filter in a stacked AW filterpackage, including a second substrate stacked on a frame on a firstsurface of a substrate to form a cavity over an AW filter circuit on asubstrate;

FIG. 4 is a flowchart illustrating a process of fabricating the stackedAW filter package in FIG. 3 , including stacking a second substrate on afirst frame on a first substrate to form a cavity over an AW filtercircuit on the first substrate;

FIG. 5A and 5B are a flowchart illustrating a process of fabricating thestacked AW filter package in FIGS. 2A-2C, including forming insulatorsbetween the outer perimeter walls of the stacked AW filters and themetal interconnects that extend between a third substrate and contactpads on a second substrate to avoid leakage current;

FIG. 6 is a top view of a frame on a surface of a substrate in the AWfilter package in FIGS. 2A-2C and 3 ;

FIG. 7 is a top perspective view of an example of an AW filter circuitas illustrated in FIGS. 2A-2C;

FIG. 8 is a block diagram of an exemplary wireless communications devicethat includes a radio frequency (RF) module including AW filter packagesincluding a first AW filter circuit on a first substrate protected in acavity by a second substrate stacked on a frame on the first substrate,and also including insulators between the first substrate and metalinterconnects extending from a contact pad on the second substrate to athird substrate stacked on a backside of the first substrate, asillustrated in FIGS. 2A-2C, 3, and 7 ; and

FIG. 9 is a block diagram of an exemplary processor-based system thatcan include AW filter packages, including a first AW filter circuit on afirst substrate protected in a cavity by a second substrate stacked on aframe on the substrate, and also including insulators between the firstsubstrate and metal interconnects extending from a contact pad on thesecond substrate to a third substrate stacked on a backside of thesubstrate, as illustrated in FIGS. 2A-2C, 3, and 7 , and according toany of the aspects disclosed herein,

DETAILED DESCRIPTION

With reference now to the drawing figures, several exemplary aspects ofthe present disclosure are described. The word “exemplary” is usedherein to mean “serving as an example, instance, or illustration.” Anyaspect described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects.

Before discussing exemplary aspects of stacked acoustic wave (AW) filterpackages of one or more AW filters that each include at least one AWfilter circuit on a first substrate and a second substrate (e.g., capsubstrate) disposed on a frame to provide a protective cavity over theAW filter circuit, as illustrated in FIGS. 2A-2C, FIG. 1 is discussed.FIG. 1 is an illustration of a surface acoustic wave (SAW) filtercircuit 100 on a first substrate 102 that may be employed in an AWfilter 104 in a stacked AW filter package. Though not shown here, the AWfilter 104 will include a second substrate disposed on a frame on thefirst substrate 102 to form a cavity to protect the AW filter circuit100 from acoustic interference, as disclosed herein. In this regard,FIG. 1 is a perspective view of the AW filter 104, which is configuredto pass certain frequency ranges while blocking other frequencies of aninput radio frequency (RF) signal. The AW filter 104 may be included inanother integrated circuit (IC) package that includes RFtransmission/reception circuity and antennas, where the SAW filtercircuit 100 is employed to filter transmitted and/or received RFsignals. The first substrate 102 includes a piezoelectric material 106forming a first surface 108 in this example. A first interdigitaltransducer (IDT) 110(1) is disposed on the first surface 108 of thefirst substrate 102 as an input circuit. A second EDT 110(2) is alsodisposed on the first surface 108 of the first substrate 102 as anoutput circuit adjacent to the first IDT 110(1). The first IDT 110(1) isconfigured to receive an input RF signal 112 through first metalinterconnects 114A, 114B coupled to first metal contacts 116A, 116B,respectively. The first metal contacts 116A, 116B (e.g., solder bumps,solder balls) on the first substrate 102 connect to the first IDT110(1). The first IDT 110(1) includes interdigitated metal interconnects118A, 118B (e.g., metal lines, metal traces) and is configured toconvert the received electrical input RE signal 112 into acoustic wavesthat propagate on the first surface 108 of the substrate 102 from thefirst IDT 110(1) to the second IDT 110(2). The first IDT 110(1) isconfigured to emit an acoustic wave on the first surface 108, and thesecond IDT 110(2) is configured to receive a filtered acoustic wave andconvert the filtered acoustic wave into a filtered RF signal 120. Thesecond IDT 110(2) includes interdigitated metal interconnects 122A, 122Bcoupled to second metal contacts 124A, 124B, respectively, which providethe filtered RE signal 120 to second metal interconnects 126A, 126B. Insome examples, a SAW substrate corresponding to the first substrate 102may include multiple SAW filter circuits 100. Similarly, a bulk acousticwave (BAW) substrate may include multiple BAW filter circuits.

Exemplary aspects disclosed herein support a multi-level stacked AWfilter package 200 as shown in a cross-sectional side view in FIGS.2A-2C, which includes a first, top AW filter 202 (“first AW filter 202”)and a second, bottom AW filter 204 (“second AW filter 204”) thatinclude, respectively, a first substrate 206 comprising at least onefirst AW filter circuit 208 disposed on a first surface 210 thereof, anda third substrate 212 comprising at least one, second AW filter circuit214 disposed on a second surface 216. The first substrate 206 and thethird substrate 212 include the first AW filter circuit 208 and thesecond AW filter circuit 214, respectively, disposed thereon. Themulti-level stacked AW filter package 200 may also be referred to hereinas the “stacked AW filter package 200” or the “AW filter package 200.”

The first AW filter circuit 208 and the second AW filter circuit 214each provide RE signal filtering. The first AW filter 202 includes afirst frame 218 coupled to the first substrate 206 and surrounding theat least one first AW filter circuit 208. A second substrate 220disposed on the first frame 218 encloses a first cavity 222 (e.g., anair cavity) above the first AW filter circuit 208, inside the firstframe 218, and between the first substrate 206 and the cap substrate220. The second substrate 220, by being disposed on the first frame 218,forms a cap structure which can also be referred to herein as “capsubstrate 220.” The second AW filter 204 includes a second frame 224coupled. to the third substrate 212 and surrounding the at least one,second AW filter circuit 214. The first substrate 206 of the first AWfilter 202 is disposed on the second frame 224 to provide a capstructure that encloses a second cavity 226 (e.g., an air cavity) insidethe second frame 224 between the first substrate 206 and the thirdsubstrate 212. In this regard, the multi-level AW filter package 200includes multiple AW filters stacked in a vertical direction in astacked arrangement to include multiple filter circuits to filtermultiple frequencies or frequency bands.

The first substrate 206 and the third substrate 212 can be formed from asemiconductor material as semiconductor substrates 213 to take advantageof semiconductor fabrication processes and techniques used infabricating semiconductor die packages that can be less expensive thanconventional processes in which substrates are formed of a piezoelectricmaterial. Fabricating the first substrate 206 and the third substrate212 includes forming semiconductor substrates 213, such as siliconsubstrates, with the first and second surfaces 210, 216 comprising apiezoelectric material 228. The piezoelectric material 228 may be anyappropriate piezoelectric material including, but not limited to,quartz, lithium tantalate (LiTaO₃), lithium niobate (LiNbO₃), aluminumnitride (AlN), scandium doped AlN (AlNSc), barium titanate (BaTiO₃), andzinc oxide (ZnO) disposed on the first and third substrates 206, 212.

In the multi-level AW filter package 200, first metal interconnects 230provide interconnect paths (“signal paths”) 232 for the first AW filter202 to receive RF signals and send filtered RF signals to a contactsurface 234 of the cap substrate 220. The first metal interconnects 230are separate from at least one second metal interconnect 236, providingsignal paths 238 for the second AW filter 204. In this regard, the firstmetal interconnects 230 are in the form of metalized verticalinterconnect accesses (vias) 240 disposed through the cap substrate 220down to the first surface 210 of the first substrate 206 to providesignal paths 232 for the first AW filter circuits 208. Further, the atleast one second metal interconnect 236 (“metal interconnect 236”) in ametallization layer 243 are formed on outer perimeter walls 244 of thestacked AW filters 202, 204 to provide the signal paths 238 for thesecond AW filter circuit 214 of the second AW filter 204, which arephysically and electrically separated from the signal paths 232 of thefirst AW filter 202. The metal interconnects 236 provide signal paths238 between the second AW filter circuit 214 and contact pads 246disposed on the contact surface 234 of the cap substrate 220 of thefirst AW filter 202. The contact pads 246 comprise a metal or metalalloy (e.g., solder) that may be formed in a pad or bump and configuredto conduct electrical signals. In this example, the metal interconnects236 formed in the metallization layer 243 are configured to distributesignals from the contact pad 246 to the first surface 210 of the firstsubstrate 206. As a non-limiting example, the metal interconnects 236may be redistribution layer (RDL) interconnects formed in one or moreRDL layers coupled to the contact pads 246, wherein the RDLinterconnects are configured to redistribute signals from the contactpad 246 to the first surface 210 of the first substrate 206. Forming thesignal paths 238 of the second AW filter 204 in the AW filter package200 as second metal interconnect 236 of the metallization layer 243 canallow, for example, metallization layer fabrication processes to beemployed to fabricate the AW filter package 200. For example if themetallization layer 243 is a RDL, a RDL fabrication process can beemployed.

Surfaces on which the metal interconnects 236 can be formed in ametallization layer fabrication process (e.g. RDL fabrication processes)include surfaces parallel to a substrate (e.g., horizontal) on a firstside (e.g., upper side) of the substrate, surfaces orthogonal to thesubstrate (e.g., vertical), or angled surfaces on the first side of thesubstrate. However, the metal interconnects 236 may not successfullyform on angled surfaces or horizontal surfaces that are on a second side(e.g., downward side) of a substrate and not exposed from a directionorthogonal to the substrate on the first side of the substrate. Forexample, an metallization layer may be formed on an upward-facingsurface and a continuous side wall surface but not on a downward-facingsurface or a side wall surface that is shadowed by an upper substrate.In this regard, to successfully fabricate a continuous metalinterconnect 236 on the outer perimeter walls 244 of the AW filter 202,204, “negative exposure” areas, such as areas in which an upperstructure overhangs a lower structure (e.g., shadowing the lowerstructure from the first side) can produce unreliable results in theformation of metallization layers 243. In an example regarding stackedstructures, a metal interconnect can be formed on an outer perimeterwall of a stack of substrates in which side surfaces of the substratesare aligned in the Z-axis direction. However, this would require thateach outer perimeter wall of the stack, on which the metal interconnectsare, be aligned in the Z-axis direction. In practice, however,manufacturing tolerances of substrates can allow substrate widths tovary and substrate overlays to vary. An upper substrate in a stackhaving a larger width than a lower substrate in the stack, andoverhanging the lower substrate on at least one side of the stack,creates a shadowed area (e.g., a negative exposure area) (e.g., in aZ-axis direction) on a second side of the overhanging upper substrate.Such a shadowed area is not exposed in a direction orthogonal to (e.g.,in a Z-axis direction) the first side of the upper substrate, so themetallization layer may not be properly formed in the shadowed area.

In this regard, in another exemplary aspect, in the example of themulti-level AW filter package 200, to support the formation of the metalinterconnects 236 on the outer perimeter walls 244 of the stacked AWfilters 202, 204 in order to provide the signal paths 238 to the secondAW filter circuit 214, a side wall surface 250 of the cap substrate 220,a side wall surface 252 of the first substrate 206, and a side wallsurface 254 of the third substrate 212 can be staggered with respect toeach other in a horizontal direction. Here, the phrase “staggered” meansthat the first substrate 206 extends in the X-axis direction beyond theside wall surface 250 of the cap substrate 220, and the third substrate212 extends in the X-axis direction beyond the side wall surface 252 ofthe first substrate 206 such that the side wall surface 252 of the firstsubstrate 206 is between the side wall surface 250 of the cap substrate220 and a side wall surface 254 of the third substrate 212 in the X-axisdirection. The staggered side wall surfaces 250, 252 create shoulderareas 256 of the first substrate 206 that extend out beyond the sidewall surface 250 (see FIG. 213 ) of the cap substrate 220 in a directionorthogonal to the side wall surface 250 of the cap substrate 220 (e.g.,in an X-axis direction). The staggered side wall surfaces 252, 254 alsocreate, in the multi-level AW filter package 200, lower shoulder areas258 on the third substrate 212 that extend out (e.g., in the X-axisdirection) beyond a side wall surface 252 of the first substrate 206 ofthe AW filter package 200. The shoulder areas 256 and lower shoulderareas 258 provide support for the formation of the metal interconnects236 on the outer perimeter walls 244 of the stacked AW filters 202, 204using, for example, RDL fabrication processes and avoid overlaps thatcreate negative exposure areas where the metal interconnect 236 may notbe able to be formed.

With further reference to FIGS. 2A-2C, the metal interconnect 236 isdisposed on the contact surface 234 of the cap substrate 220 and iselectrically coupled to the contact pad 246. The contact pad 246 isconfigured to couple to an external circuit to receive an RF signal orprovide a filtered RF signal. A signal received or generated on thecontact pad 246 may be electrically coupled, through the metalinterconnect 236, to one of the second AW filter circuits 214 on thethird substrate 212. In this regard, the metal interconnect 236continues from the contact surface 234 (e.g., a top surface of the AWfilter package 200) onto the side wall surface 250 of the cap substrate220. The side wall surface 250 of the cap substrate 220 extendsvertically (e.g., in the Z-axis direction), which is orthogonal to thecontact surface 234. The first frame 218 is disposed between the capsubstrate 220 and the first surface 210 of the first substrate 206. Aside wall surface 260 of the first frame 218 may extend (e.g., in theZ-axis direction) in alignment with the side wall surface 250 of the capsubstrate 220 without deviating in a direction orthogonal (e.g., X-axisdirection) with respect to the side wall surface 250 of the capsubstrate 220. In this manner, the side wall surface 250 of the capsubstrate 220 and the side wall surface 260 of the first frame 218 canallow the metal interconnect 236 to be formed by, for example, RDLfabrication processes or other metallization layer fabricationprocesses. The metal interconnect 236 extends from the side wall surface250 of the cap substrate 220 onto the side wall surface 260 of the firstframe 218 between the cap substrate 220 and the first substrate 206. Thefirst frame 218 extends from the side wall surface 250 of the capsubstrate 220 in a direction (X-axis direction) orthogonal to the sidewall surface 250 of the cap substrate 220 on a first side S₁ (i.e., intothe first cavity 222) of the side wall surface 250 of the cap substrate220 to support the cap substrate 220. The first frame 218 comprises adifferent material than the cap substrate 220. In some examples, thefirst frame 218 is a polymer material formed on one of the capsubstrates 220, and the first substrate 206 before the cap substrate 220is stacked on the first substrate 206. The cap substrate 220 may beformed of glass, for example.

In some examples, the first frame 218 extends in the directionorthogonal to the side wall surface 250 of the cap substrate 220 on asecond side S₂ of the side wall surface 250 of the cap substrate 220onto the shoulder area 256 on the first surface 210 of the firstsubstrate 206. In this regard, the side wall surface 260 of the firstframe 218 is not aligned with the side wall surface 250 of the capsubstrate 220 such that the side wall surface 260 of the first frame 218is staggered with respect to the side wall surface 250 of the capsubstrate 220, which also allows for formation of the metal interconnect236. In such examples, the metal interconnect 236 is also disposed on atop surface 262 of the first frame 218. Thus, the metal interconnect 236extends, in such examples, from the side wall surface 250 of the capsubstrate 220 onto the top surface 262 of the first frame 218 and ontothe side wall surface 260 of the first frame 218.

Following the metal interconnect 236 in the Z-axis direction along theouter perimeter walls 244 toward the third substrate 212, the metalinterconnect 236 is disposed on the shoulder area 256 of the firstsubstrate 206 and onto the side wall surface 252 of the first substrate206. The side wall surface 252 of the first substrate 206 may beorthogonal to the first surface 210 of the first substrate 206. Thesecond frame 224 is disposed between the first substrate 206 and thethird substrate 212. A side wall surface 264 of the second frame 224 maybe in alignment with the side wall surface 252 of the first substrate206, making it possible to form metal interconnect 236 extending fromthe side wall surface 252 of the first substrate 206 and continue ontothe side wall surface 264 of the second frame 224. The second frame 224extends from the side wall surface 252 of the first substrate 206 in thedirection (e.g., X-axis direction) orthogonal to the side wall surface252 of the first substrate 206 to the first side S₁ (i.e., into thesecond cavity 226) to support the first substrate 206.

In some examples, the second frame 224 extends in the directionorthogonal to the side wall surface 252 of the first substrate 206 tothe second side S₂ of the side wall surface 252 of the first substrate206, so as to be staggered with respect to the side wall surface 252 ofthe first substrate 206 (i.e., the side wall surface 264 of the secondframe 224 extends in the X-axis direction to the side S₂ of the sidewall surface 252 of the first substrate 206). In such examples, themetal interconnect 236 is disposed on a top surface 266 of the secondframe 224, continues onto the side wall surface 264 of the second frame224, and is also disposed onto the lower shoulder area 258 of the thirdsubstrate 212, which is also on the second side S₂ of the side wallsurface 264 of the second frame 224.

To electrically couple the contact pad 246 to a second AW filter circuit214 on the second surface 216 by way of the metal interconnect 236, themetal interconnect 236 coupled to the contact pad 246 is also coupled asurface interconnect 268. The surface interconnect 268 is disposed onthe second surface 216 of the third substrate 212 and extends frominside the second cavity 226 to the lower shoulder area 258 (outside thecavity). The surface interconnect 268 is coupled to both the second AWfilter circuit 214 and the metal interconnect 236. The second frame 224is disposed onto a portion of the surface interconnect 268 between thesecond AW filter circuit 214 inside the second cavity 226 and the metalinterconnect 236 on the lower shoulder area 254. In this manner, themetal interconnect 236 electrically couples the second AW filter circuit214 to the contact pad 246.

In another exemplary aspect, in the multi-level stacked AW filterpackage 200, in which the metal interconnects 236 provide the signalpath 238 between the contact pads 246 and the second AW filtercircuit(s) 214 on the third substrate 212, where the metal interconnects236 extend across the first substrate 206 including first AW filtercircuits 208, an insulator 270 is disposed on the side wall surface 252of the first substrate 206 between the side wall surface 252 of thefirst substrate 206 and the metal interconnect 236. The first substrate206 comprises one of the semiconductor substrate 213 with apiezoelectrical material 228 on the first surface 210. The piezoelectricmaterial 228 protects the semiconductor substrate 213, which is asemiconductor, from electrical signals in the metal interconnect 236. Infabrication, the semiconductor substrate 213 is diced from a wafer, andthe side wall surface 252 of the first substrate 206 is exposed (e.g.,unprotected from electrical signals). Thus, disposing the metalinterconnect 236 directly onto the side wall surface 252 of the firstsubstrate 206, in which the at least one first AW filter circuit(s) 208are formed, would cause the first AW filter circuits 208 to beelectrically coupled to the metal interconnect 236 and, therefore, tothe second AW filter circuits 214 and the contact pads 246. As a resultof such electrical coupling, a current may leak through thesemiconductor substrate 213 between the first AW filter circuits 208 andthe second AW filter circuits 214, which can cause interference with theoperation of the first and second AW filter circuits 208, 214, and alsocause power loss in the AW filter package 200. In this regard, theinsulator 270 is disposed on the side wall surface 252 of the firstsubstrate 206 between the side wall surface 252 of the first substrate206 and the metal interconnect 236 to insulate and isolate the first AWfilter circuits 208 from the second AW filter circuits 214. Infabrication, the insulator 270 is disposed on the outer perimeter walls244 of the stacked AW filters 202, 204, including the side wall surface250 of the cap substrate 220, the side wall surface 260 of the firstframe 218, and on the first surface 210 of the first substrate 206,before the metal interconnect 236 is disposed thereon. Thus, theinsulator 270 is disposed between the side wall surface 250 of the capsubstrate 220 and the metal interconnect 236, between the side wallsurface 260 of the first frame 218 and the metal interconnect 236, andbetween the first surface 210 of the first substrate 206 and the metalinterconnect 236.

In another aspect, the first metal interconnects 230 (i.e., the vias240) and the second metal interconnects 236 also provide separatethermal paths for distributing heat away from the first and second AWfilter circuits 208, 214 and to the contact surface 234 of the capsubstrate 220 to be dissipated from the AW filter package 200. Formingthe vias 240 in the cap substrate 220 may include, for example, laserdrilling holes in the cap substrate 220 and filling the holes with metalto provide both electrical and thermal conduction. The vias 240 may beformed of copper, aluminum, or other metal or metals that provideelectrical and thermal conductivity.

In another aspect, an objective of the multi-level stacked AW filterpackage 200 is to save area in an electronic device, but an area savingsis not beneficial unless the resulting increase in height is acceptablefor use in the electronic device. In this regard, by forming the firstsubstrate 206 and the third substrate 212 of semiconductor substrates213, which can be processed by IC processing methods, the firstsubstrate 206 and the third substrate 212 can be thinned to reducepackage height. In addition, forming the cap substrate 220 of glassprovides additional structural integrity to the AW filter package 200that would not be provided by more flexible capping materials, such as apolymer. As an example, the third substrate 212 may have a thicknessT₂₁₂ in a first direction orthogonal to the second surface 216 in arange of sixty (60) microns (μm) to one hundred thirty (130) μm, thefirst substrate 206 may have a thickness T₂₀₆ in the first direction ina range of thirty (30) μm to seventy (70) μm, and the cap substrate 220may have a thickness T₂₂₀ in a range of thirty (30) μm to seventy (70)μm. In some examples, the thickness T₂₁₂ of the third substrate 212 isless than eighty-five (85) μm, the thickness T₂₀₆ is less thanfifty-five (55) μm, and the thickness T₂₂₀ of the cap substrate 220 isless than fifty-five (55) μm.

Exemplary aspects disclosed herein supporting a multi-level stacked AWfilter package 200 as shown in FIGS. 2A-2C can also be employed in astacked AW filter package 300, as shown in FIG. 3 , that includes only asingle AW filter 302 including a first substrate 304, an AW filtercircuit 306 on a first surface 308 of the first substrate 304, a frame310 disposed on the first surface 308, and a second substrate 312disposed (e.g., stacked) on the frame 310. The second substrate 312, bybeing disposed on the frame 310, forms a cap structure which can also bereferred to herein as “cap substrate 312.” In this regard, ametallization fabrication process may be used to fabricate ametallization layer 313 comprising at least one metal interconnect 314(“metal interconnects 314”). As a non-limiting example, themetallization layer 312 can be a RDL with RDL interconnects therein,providing signal paths 316 of the AW filter 302 even in an AW filterpackage 300 that does not include stacked AW filters. The metalinterconnects 314 provide signal paths 316 (and thermal paths) from thefirst substrate 304 to contact pads 318 on a contact surface 320 of thecap substrate 312. The metal interconnects 314 are disposed on thecontact surface 320 and are electrically coupled to the contact pads318, and are also coupled to the first surface 308 of the firstsubstrate 304.

In order to employ metallization fabrication processes, such as RDLfabrication methods as a non-limiting example, a side wall surface 322of the first substrate 304 is staggered with respect to a side wallsurface 324 of the cap substrate 312, as in the multi-level AW filterpackage 200 discussed above. Thus, the first surface 308 includes ashoulder area 326 that extends in a direction orthogonal to a side wallsurface 324 of the cap substrate 312. The metal interconnects 314 extendonto the side wall surface 324 of the cap substrate 312. In an examplein which a side wall surface 328 of the frame 310 is aligned (e.g.,along an axis in the Y-axis direction) with the side wall surface 324 ofthe cap substrate 312, the metal interconnect 314 extends from the sidewall surface 324 of the cap substrate 312 onto the side wall surface 328of the frame 310. The frame 310 extends from the side wall surface 324of the cap substrate 312 to a first side S₁ between the cap substrate312 and the first substrate 304 to support the cap substrate 312 andprovide a cavity 330. In some examples, the frame 310 is not alignedwith the side wall surface 324 of the cap substrate 312. Instead, theframe 310 extends beyond the side wall surface 324 of the cap substrate312 in a direction orthogonal to the side wall surface 324 of the capsubstrate 312 to a second side S₂ of the side wall surface 324 of thecap substrate 312 onto the shoulder area 326 of the first substrate 304,such that the side wall surface 328 of the frame 310 is staggered withrespect to the side wall surface 324 of the cap substrate 312. In thisexample, the metal interconnect 314 extends from the side wall surface324 of the cap substrate 312 onto a top surface 332 of the frame 310 andonto the side wall surface 328 of the frame 310. The metal interconnect314 is disposed onto the first surface 308 of the first substrate 304. Asurface interconnect 334 disposed on the first surface 308 extends fromwithin the cavity 330, where the surface interconnect 334 iselectrically coupled to the AW filter circuit 306, past the frame 310,and into the shoulder area 326. The metal interconnect 314 iselectrically coupled to the surface interconnect 334 in the shoulderarea 326 to electrically couple the AW filter circuit 306 to the contactpad 318.

FIG. 4 is a flow chart of a process 400 of fabricating the stacked AWfilter package 300. The process 400 includes forming a first substrate304 comprising a first surface 308 (block 402) and forming an AW filtercircuit 306 on the first surface 308 of the first substrate 304 (block404). The process 400 includes forming a frame 310 on the first surface308 of the first substrate 304 (block 406) and forming a secondsubstrate (e.g., cap substrate) 312 comprising a contact surface 320 anda side wall surface 324 (block 408). The process 400 includes disposingthe cap substrate 312 on the frame 310 to form a cavity 330 between theAW filter circuit 306 and the cap substrate 312 (block 410) and forminga metallization layer 313 comprising at least one metal interconnect 314coupled to the contact surface 320 of the cap substrate 312 and thefirst surface 308 of the first substrate 304, the at least one metalinterconnect 314 disposed on the side wall surface 324 of the capsubstrate 312 (block 412).

FIGS. 5A and 5B are a flow chart of a process 500 of fabricating astacked AW filter package 200. The process 500 includes forming a firstsubstrate 206 comprising a first surface 210 and a side wall surface 252(block 502) and forming a first AW filter circuit 208 on the firstsurface 210 of the first substrate 206 (block 504). The process 500includes forming a first frame 218 on the first surface 210 of the firstsubstrate 206 (block 506) and forming a cap substrate 220 comprising acontact surface 234 and a side wall surface 250 (block 508). The process500 includes disposing the cap substrate 220 on the first frame 218 toform a first cavity 222 between the first AW filter circuit 208 and thecap substrate 220 (block 510) and forming a third substrate 212comprising a second AW filter circuit 214 on a second surface 216 of thethird substrate 212 (block 512). The process 500 includes forming asecond frame 224 on the second surface 216 of the third substrate 212(block 514) and disposing the first substrate 206 on the second frame224 to form a second cavity 226 between the second AW filter circuit 214and the first substrate 206 (block 516). The process 500 includesforming an insulator 268 on the side wall surface 256 of the firstsubstrate 206 (block 518) and forming metallization layer 243 comprisingat least one metal interconnect (236 coupled to the contact surface 234of the cap substrate 220 and the second surface 216 of the thirdsubstrate 212, the at least one metal interconnect (236 disposed on theinsulator 270 on the side wall surface 252 of the first substrate 206(block 520).

FIG. 6 is an illustration of a top view of an example of a frame 600that supports the fabrication of stacked AW filter packages 200 and 300.The frame 600 may correspond to the frames 218 and 224 in FIGS. 2A-2Cand frame 310 in FIG. 3 . The frame 600 includes a perimeter frame 602extending along a perimeter 604 of a first substrate 606, which islarger in the X-axis direction and the Y-axis direction, such that thefirst substrate 606 includes a shoulder area 608 that is staggered inwidth with respect to the frame 600. In some examples, the dimensions ofthe frame 600 may be the same size or slightly larger in area than asecond substrate (e.g., cap substrate) to avoid “negative exposure”areas in which a metal interconnect may not be formed. The perimeterframe 602 in this example is rectangular but may be square or anothershape corresponding to a perimeter of a second substrate to besupported. The frame 600 includes frame members 610 to support a secondsubstrate against pressure on a contact surface by providing additionalsupport so a size of a cavity 612 may be increased to include more AWfilter circuits 614 on the first substrate 606. The frame members 610extend across the cavity 612 from the perimeter frame 602. The framemembers 610 may be linear, having a first end 616 in contact with andextending from the perimeter frame 602. The frame members 610 includesecond ends 618 in the cavity and not in contact with the perimeterframe 602. The cavity 612 continues (i.e., without interruption) aroundthe second ends 618 from a first cavity section 620A on a first side ofthe frame member 610 to a second cavity section 620B on a second side ofthe frame member 610. An AW filter circuit 614 may be disposed in thefirst cavity section 620A. In some examples, another AW filter circuit624 may be disposed in the second cavity section 620B. As shown, theframe 600 includes a plurality of the frame members 610 extending intothe cavity 612 from the perimeter frame 602 to support the secondsubstrate.

The perimeter frame 602 and the frame members 610 are in contact with asecond substrate (not shown) and the first substrate 606. The framemembers 610 support a stacked AW filter package by providing moresupport within the cavity 612 against pressure to the contact surface ofa first substrate. Pressure applied to the first substrate, which may bea glass substrate, can cause inward deflection of the glass and a topsubstrate in a stacked AW filter package. In areas of the cavity 612 inwhich the frame members 610 are excluded (i.e., there are no framemembers 610), the glass can deflect under pressure to a breaking pointif such unsupported areas are too large. However, due to the structuralrigidity of a glass second substrate, the cavity 612 of the AW filterpackages, as disclosed herein, may include a circular region 626 havinga diameter up to 400 μm in which the perimeter frame 602 and the framemembers 610 are excluded. In some examples, the circular region 626 hasa diameter (D1) in a range between 360 μm and 400 μm.

FIG. 7 is a top perspective view of a stacked AW filter package 700. Thestacked NW filter package 700 includes a second substrate 702 stackedabove a first substrate 704 to form a first AW filter 706. The secondsubstrate 702, by being disposed above the first substrate 704, forms acap structure which can also be referred to herein as “cap substrate702.” The first AW filter 706 also provides a cap structure as stackedon a third substrate 708 to form a second AW filter 710. The stacked AWfilter package 700 includes contact pads 712 on the cap substrate 702.The contact pads 712 couple to the first metal interconnects 714, whichcomprise vias 716 that extend through the cap substrate 702 to couple tofirst AW filter circuits (not shown) on the first substrate 704. Secondmetal interconnects 718 (which may be RDL interconnects) extend from thecontact pads 712 along outer perimeter walls 720 to the second AW filter710. The second metal interconnects 718 are disposed on insulators 722on a side wall surface 724 of the first substrate 704 to couple thecontact pads 712 to second AW filter circuits (not shown) on the thirdsubstrate 708 without electrically coupling to the semiconductormaterial of the first substrate 704.

FIG. 8 illustrates an exemplary wireless communications device 800 thatincludes RF components formed from one or more ICs 802 and can includestacked AW filter packages 803. The stacked AW filter packages 803include a first AW filter circuit disposed on a first substrate, asecond substrate disposed on a first frame disposed on the firstsubstrate, and the first substrate disposed on a second frame disposedon a third substrate to enclose a second, bottom AW filter circuit,wherein contact pads on the second substrate are electrically coupled tothe second AW filter circuit by metal interconnects disposed oninsulators to protect against leakage currents to the first substrate,as illustrated in FIGS. 2A-2C, 3 and 7 , and according to any of theaspects disclosed herein. The wireless communications device 800 mayinclude or be provided in any of the above-referenced devices, asexamples. As shown in FIG. 8 , the wireless communications device 800includes a transceiver 804 and a data processor 806. The data processor806 may include a memory to store data and program codes. Thetransceiver 804 includes a transmitter 808 and a receiver 810 thatsupport bi-directional communications. In general, the wirelesscommunications device 800 may include any number of transmitters 808and/or receivers 810 for any number of communication systems andfrequency bands. All or a portion of the transceiver 804 may beimplemented on one or more analog ICs, RFICs, mixed-signal ICs, etc.

The transmitter 808 or the receiver 810 may be implemented with asuper-heterodyne architecture or a direct-conversion architecture. Inthe super-heterodyne architecture, a signal is frequency-convertedbetween RF and baseband in multiple stages, e.g., from RF to anintermediate frequency (IF) in one stage and then from IF to baseband inanother stage. In the direct-conversion architecture, a signal isfrequency-converted between RF and baseband in one stage. Thesuper-heterodyne and direct-conversion architectures may use differentcircuit blocks and/or have different requirements. In the wirelesscommunications device 800 in FIG. 8 , the transmitter 808 and thereceiver 810 are implemented with the direct-conversion architecture.

In the transmit path, the data processor 806 processes data to betransmitted and provides I and Q analog output signals to thetransmitter 808. In the exemplary wireless communications device 800,the data processor 806 includes digital-to-analog converters (DACs)812(1), 812(2) for converting digital signals generated by the dataprocessor 806 into the I and Q analog output signals, e.g., I and Qoutput currents, for further processing.

Within the transmitter 808, lowpass filters 814(1), 814(2) filter the Iand Q analog output signals, respectively, to remove undesired signalscaused by the prior digital-to-analog conversion. The lowpass filters814(1), 814(2) may be implemented as AW filter packages 803. Amplifiers(AMPS) 816(1), 816(2) amplify the signals from the lowpass filters814(1), 814(2), respectively, and provide I and Q baseband signals. Anupconverter 818 upconverts the I and Q baseband signals with I and Qtransmit (TX) local oscillator (LO) signals from a TX LO signalgenerator 822 through mixers 820(1), 820(2) to provide an upconvertedsignal 824. A filter 826 filters the upconverted signal 824 to removeundesired signals caused by the frequency upconversion as well as noisein a receive frequency band. A power amplifier (PA) 828 amplifies theupconverted signal 824 from the filter 826 to obtain the desired outputpower level and provides a transmit RF signal. The transmit RE signal isrouted through a duplexer or switch 830 and transmitted via an antenna832. Any of the lowpass filters 814(1) and 814(2), or the filter 826,may be an acoustic wave filter (AW filter) packages 803.

In the receive path, the antenna 832 receives signals transmitted bybase stations and provides a received RF signal, which is routed throughthe duplexer or switch 830 and provided to a low noise amplifier (LNA)834. The duplexer or switch 830 is designed to operate with a specificreceive (RX)-to-TX duplexer frequency separation, such that RX signalsare isolated from TX signals. The received RF signal is amplified by theLNA 834 and filtered by a filter 836 to obtain a desired RF inputsignal. Downconversion mixers 838(1), 838(2) mix the output of thefilter 836 with I and Q RX LO signals (i.e., LO_I and LO_Q) from an RXLO signal generator 840 to generate I and Q baseband signals. The I andQ baseband signals are amplified by AMPs 842(1), 842(2) and furtherfiltered by lowpass filters 844(1), 844(2) to obtain I and Q analoginput signals, which are provided to the data processor 806. Any of thefilter 836 and the lowpass filters 844(1), 844(2) may be AW filterpackages 803. In this example, the data processor 806 includesanalog-to-digital converters (ADCs) 846(1), 846(2) for converting theanalog input signals into digital signals to be further processed by thedata processor 806.

In the wireless communications device 800 of FIG. 8 , the TX LO signalgenerator 822 generates the I and Q TX LO signals used for frequencyupconversion, while the RX LO signal generator 840 generates the I and QRX LO signals used for frequency downconversion. Each LO signal is aperiodic signal with a particular fundamental frequency. A TXphase-locked loop (PLL) circuit 848 receives timing information from thedata processor 806 and generates a control signal used to adjust thefrequency and/or phase of the TX LO signals from the TX LO signalgenerator 822. Similarly, an RX PLL circuit 850 receives timinginformation from the data processor 806 and generates a control signalused to adjust the frequency and/or phase of the RX LO signals from theRX LO signal generator 840.

Wireless communications devices 800 that can each include stacked AWfilter packages 803 including a second substrate stacked on a firstsubstrate comprising a first AW filter circuit further stacked on athird substrate comprising a second AW filter circuit, wherein contactpads on the second substrate are electrically coupled to the second AWfilter circuit by metal interconnects disposed on insulators to protectagainst leakage currents to the first substrate, as illustrated in FIGS.2A-2C, 3 and 7 , and according to any of the aspects disclosed herein,may be provided in or integrated into any processor-based device.Examples, without limitation, include a set-top box, an entertainmentunit, a navigation device, a communications device, a fixed locationdata unit, a mobile location data unit, a global positioning system(GPS) device, a mobile phone, a cellular phone, a smartphone, a sessioninitiation protocol (SIP) phone, a tablet, a phablet, a server, acomputer, a portable computer, a mobile computing device, a wearablecomputing device (e.g., a smartwatch, a health or fitness tracker,eyewear, etc.), a desktop computer, a personal digital assistant (PDA),a monitor, a computer monitor, a television, a tuner, a radio, asatellite radio, a music player, a digital music player, a portablemusic player, a digital video player, a video player, a digital videodisc (DVD) player, a portable digital video player, an automobile, avehicle component, avionics systems, a drone, and a multicopter.

In this regard, FIG. 9 illustrates an example of a processor-basedsystem 900 including RF circuits including stacked AW filter packages901. The stacked AW filter packages 901 include a first AW filtercircuit disposed on a first substrate, a second substrate disposed on afirst frame disposed on the first substrate, and the first substratedisposed on a second frame disposed on a third substrate to enclose asecond, bottom AW filter circuit, wherein contact pads on the secondsubstrate are electrically coupled to the second AW filter circuit bymetal interconnects disposed on insulators to protect against leakagecurrents to the first substrate, as illustrated in FIGS. 2A-2C, 3, and 7, and according to any aspects disclosed herein. In this example, theprocessor-based system 900 includes one or more central processor units(CPUs) 902, which may also be referred to as CPU or processor cores,each including one or more processors 904. The CPU(s) 902 may have cachememory 906 coupled to the processor(s) 904 for rapid access totemporarily stored data. The CPU(s) 902 is coupled to a system bus 908and can intercouple master and slave devices included in theprocessor-based system 900. As is well known, the CPU(s) 902communicates with these other devices by exchanging address, control,and data information over the system bus 908. For example, the CPU(s)902 can communicate bus transaction requests to a memory controller 910as an example of a slave device. Although not illustrated in FIG. 9 ,multiple system buses 908 could be provided; wherein each system bus 908constitutes a different fabric.

Other master and slave devices can be connected to the system bus 908.As illustrated in FIG. 9 , these devices can include a memory system 912that includes the memory controller 910 and one or more memory arrays914, one or more input devices 916, one or more output devices 918, oneor more network interface devices 920, and one or more displaycontrollers 922, as examples. Each of the memory system 912, the one ormore input devices 916, the one or more output devices 918, the one ormore network interface devices 920, and the one or more displaycontrollers 922 can include RF circuits including stacked AW filterpackages 901. The stacked AW filter packages 901 include a first AWfilter circuit disposed on a first substrate, a second substratedisposed on a first frame disposed on the first substrate, and the firstsubstrate disposed on a second frame disposed on a third substrate toenclose a second, bottom AW filter circuit, wherein contact pads on thesecond substrate are electrically coupled to the second AW filtercircuit by metal interconnects disposed on insulators to protect againstleakage currents to the first substrate, as illustrated in FIGS. 2A-2C,3, and 7 , and according to any of the aspects disclosed herein. Theinput device(s) 916 can include any type of input device, including, butnot limited to, input keys, switches, voice processors, etc. The outputdevice(s) 918 can include any type of output device, including, but notlimited to, audio, video, other visual indicators, etc. The networkinterface device(s) 920 can be any device configured to allow anexchange of data to and from a network 924. The network 924 can be anytype of network, including, but not limited to, a wired or wirelessnetwork, a private or public network, a local area network (LAN), awireless local area network (WLAN), a wide area network (WAN), aBLUETOOTH™ network, and the Internet. The network interface device(s)920 can be configured to support any type of communications protocoldesired.

The CPU(s) 902 may also be configured to access the displaycontroller(s) 922 over the system bus 908 to control information sent toone or more displays 926. The display controller(s) 922 sendsinformation to the display(s) 926 to be displayed via one or more videoprocessors 928, which process the information to be displayed into aformat suitable for the display(s) 926. The display(s) 926 can includeany type of display, including, hut not limited to, a cathode ray tube(CRT), a liquid crystal display (LCD), a plasma display, alight-emitting diode (LED) display, etc. The display controller(s) 922,display(s) 926, and/or the video processor(s) 928 can include RFcircuits including stacked AW filter packages 901. The stacked AW filterpackages 901 include a first AW filter circuit disposed on a firstsubstrate, a second substrate disposed on a first frame disposed on thefirst substrate, and the first substrate disposed on a second framedisposed on a third substrate to enclose a second, bottom AW filtercircuit, wherein contact pads on the second substrate are electricallycoupled to the second AW filter circuit by metal interconnects disposedon insulators to protect against leakage currents to the firstsubstrate, as illustrated in FIGS. 2A-2C, 3, and 7 , and according toany of the aspects disclosed herein.

Those of skill in the art will further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithms describedin connection with the aspects disclosed herein may be implemented aselectronic hardware, instructions stored in memory or in anothercomputer-readable medium and executed by a processor or other processingdevice, or combinations of both. The master and slave devices describedherein may he employed in any circuit, hardware component, IC, or ICchip, as examples. Memory disclosed herein may be any type and size ofmemory and may be configured to store any type of information desired.To clearly illustrate this interchangeability, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. How such functionalityis implemented depends upon the particular application, design choices,and/or design constraints imposed on the overall system. Skilledartisans may implement the described functionality in varying ways foreach particular application, but such implementation decisions shouldnot be interpreted as causing a departure from the scope of the presentdisclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implemented orperformed with a processor, a Digital Signal Processor (DSP), anApplication Specific Integrated Circuit (ASC), a Field Programmable GateArray (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A processormay be a microprocessor, but in the alternative, the processor may beany conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices (e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration).

The aspects disclosed herein may be embodied in hardware and ininstructions that are stored in hardware and may reside, for example, inRandom Access Memory (RAM), flash memory, Read-Only Memory (ROM),Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, a hard disk, a removable disk, aCD-ROM, or any other form of computer-readable medium known in the art.An exemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a remote station. In the alternative, theprocessor and the storage medium may reside as discrete components in aremote station, base station, or server.

It is also noted that the operational steps described in any of theexemplary aspects herein are described to provide examples anddiscussion. The operations described may be performed in numerousdifferent sequences other than the illustrated sequences. Furthermore,operations described in a single operational step may actually beperformed in a number of different steps. Additionally, one or moreoperational steps discussed in the exemplary aspects may be combined. Itis to be understood that the operational steps illustrated in theflowchart diagrams may be subject to numerous different modifications aswill be readily apparent to one of skill in the art. Those of skill inthe art will also understand that information and signals may berepresented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations. Thus, the disclosure is not intended to belimited to the examples and designs described herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

Implementation examples are described in the following numbered clauses:

1. A stacked acoustic wave (AW) filter package, comprising:

-   -   a first substrate comprising a first surface;    -   an AW filter circuit on the first surface of the first        substrate;    -   a frame disposed on the first surface of the first substrate;    -   a second substrate comprising a contact surface and a side wall        surface, the second substrate disposed on the frame to form a        cavity between the AW filter circuit and the second substrate;        and    -   a metallization layer comprising at least one metal interconnect        coupled to the contact surface of the second substrate and the        first surface of the first substrate, the at least one metal        interconnect disposed on the side wall surface of the second        substrate.

2. The stacked AW filter package of clause 1, further comprising acontact pad coupled to the contact surface;

-   -   the at least one metal interconnect configured to redistribute        signals from the contact pad to the first surface of the first        substrate.

3. The stacked AW filter package of clause 1 or clause 2, wherein:

-   -   the frame is disposed between the second substrate and the first        surface of the first substrate, extending from the side wall        surface of the second substrate in a direction orthogonal to the        side wall surface of the second substrate on a first side of the        side wall surface of the second substrate; and    -   the first surface of the first substrate includes a shoulder        area on a second side of the side wall surface of the second        substrate in the direction orthogonal to the side wall surface        of the second substrate.

4. The stacked AW filter package of clause 3, wherein:

-   -   the at least one metal interconnect is disposed on the shoulder        area of the first surface of the first substrate.

5. The stacked AW filter package of any of clauses 1-4, furthercomprising a contact pad on the contact surface, the contact padconfigured to couple to an external circuit, wherein the at least onemetal interconnect is electrically coupled to the contact pad.

6. The stacked AW filter package of any of clauses 2-5, furthercomprising a surface interconnect on the first surface of the firstsubstrate extending from inside the cavity to the shoulder area, thesurface interconnect electrically coupled to the AW filter circuit, andthe at least one metal interconnect of the metallization layer on theshoulder area.

7. The stacked AW filter package of any of clauses 1-6, wherein the atleast one metal interconnect of the metallization layer is disposed on aside surface of the frame between the second substrate and the firstsubstrate.

8. The stacked AW filter package of any of clauses 2-7, wherein:

-   -   the frame extends in the direction orthogonal to the side wall        surface of the second substrate into the shoulder area on the        second side of the side wall surface of the second substrate;        and    -   the at least one metal interconnect of the metallization layer        is disposed on a top surface of the frame.

9. The stacked AW filter package of any of clauses 1-8, wherein theframe comprises a first material, and the second substrate comprises asecond material different than the first material,

10. The stacked AW filter package of any of clauses 1-9, wherein:

-   -   the frame comprises a polymer material;    -   the second substrate comprises a glass; and    -   the first substrate comprises a semiconductor material

11. The stacked AW filter package of any of clauses 1-10, wherein:

-   -   the frame further comprises a perimeter frame disposed along a        perimeter of the second substrate; and    -   the cavity is surrounded by e perimeter frame.

12. The stacked AW filter package of clause 11, wherein the framefurther comprises a frame member extending into the cavity, orthogonalto at least a portion of the perimeter frame.

13. The stacked AW filter package of clause 12, wherein the frame membercomprises one of a plurality of frame members of the frame.

14. The stacked AW filter package of clause 12 or clause 13, the framemember further comprising a linear frame member comprising a first endcoupled to the perimeter frame.

15. The stacked AW filter package of clause 14, the cavity comprising acontinuous cavity extending from a first cavity section on a first sideof the linear frame member and around a second end of the linear framemember to a second cavity section on a second side of the linear framemember.

16. The stacked AW filter package of clause 15, wherein:

-   -   the AW filter circuit on the first surface of the first        substrate is a first AW filter circuit;    -   the first AW filter circuit is disposed in the first cavity        section on the first side of the linear frame member; and    -   the stacked AW filter package further comprises another AW        filter circuit on the second side of the linear frame member.

17. The stacked A filter package of any of clauses 1-16, wherein thecavity comprises a continuous circular region having a diameter up to400 micrometers (μm) from which the frame is excluded.

18. The stacked AW filter package of any of clauses 1-17, wherein thediameter of the continuous circular region is greater than 360 μm.

19. The stacked AW filter package of clause 5, the stacked AW filterpackage further comprising:

-   -   a third substrate comprising a second AW filter circuit on a        second surface of the third substrate; and    -   a second frame disposed on the second surface of the third        substrate;    -   wherein:    -   the first substrate is disposed on the second frame to form a        second cavity between the second AW filter circuit and the first        substrate.

20. The stacked AW filter package of clause 19, wherein:

-   -   the first substrate further comprises a side wall surface        orthogonal to the first surface of the first substrate;    -   the second frame is disposed between the first substrate and the        second surface of the third substrate, extending from the side        wall surface of the first substrate in a direction orthogonal to        the side wall surface of the first substrate on a first side of        the side wall surface of the first substrate; and    -   the second surface of the third substrate includes a lower        shoulder area on a second side of the side wall surface of the        first substrate in the direction orthogonal to the first side        wall surface of the first substrate.

21. The stacked AW filter package of clause 20, wherein:

-   -   the at least one metal interconnect is disposed on:        -   the side wall surface of the first substrate; and        -   the lower shoulder area of the second surface of the third            substrate.

22. The stacked AW filter package of clause 21, further comprising asurface interconnect on the second surface of the third substrateextending from inside the second cavity to the lower shoulder area, thesurface interconnect electrically coupled to the second AW filtercircuit, and the at least one metal interconnect on the lower shoulderarea.

23. The stacked AW filter package of any of clauses 19-22, wherein theat least one metal interconnect is disposed on a side surface of thesecond frame between the first substrate and the third substrate.

24. The stacked AW filter package of any of clauses 20-23, wherein:

-   -   the second frame extends in the direction orthogonal to the side        wall surface of the first substrate onto the lower shoulder area        on the second side of the side wall surface of the first        substrate; and    -   the at least one metal interconnect is disposed on a top surface        of the second frame.

25. A method of fabricating a stacked acoustic wave (AW) filter package,the method comprising:

-   -   forming a first substrate comprising a first surface;    -   forming an AW filter circuit on the first surface of the first        substrate;    -   forming a frame on the first surface of the first substrate;    -   forming a second substrate comprising a contact surface and a        side wall surface;    -   disposing the second substrate on the frame to form a cavity        between the AW filter circuit and the second substrate; and    -   forming a metallization layer comprising at least one metal        interconnect coupled to the contact surface of the second        substrate and the first surface of the first substrate, the at        least one metal interconnect disposed on the side wall surface        of the second substrate.

26. The method of clause 25, further comprising:

-   -   disposing the frame between the second substrate and the first        surface of the first substrate, and extending from the side wall        surface of the second substrate in a direction orthogonal to the        side wall surface of the second substrate on a first side of the        side wall surface of the second substrate; and    -   forming a shoulder area of the first surface of the first        substrate on a second side of the side wall surface of the        second substrate in the direction orthogonal to the side wail        surface of the second substrate.

27. A stacked acoustic wave (AW) filter package, comprising:

-   -   a first substrate comprising a first surface and a side wall        surface;    -   a first AW filter circuit on the first surface of the first        substrate;    -   a first frame disposed on the first surface of the first        substrate;    -   a second substrate comprising a contact surface and a side wall        surface, the second substrate disposed on the first frame to        form a first cavity between the first AW filter circuit and the        second substrate;    -   a third substrate comprising a second AW filter circuit on a        second surface of the third substrate;    -   a second frame disposed on the second surface of the third        substrate;    -   the first substrate disposed on the second frame to form a        second cavity between the second AW filter circuit and the first        substrate;    -   a metallization layer comprising at least one metal interconnect        coupled to the contact surface of the second substrate and the        second surface of the third substrate, the at least one metal        interconnect disposed on the side wall surface of the first        substrate; and    -   an insulator disposed on the side wall surface of the first        substrate between the side wall surface of the first substrate        and the at least one metal interconnect.

28. The stacked AW filter package of clause 27, wherein the insulator isdisposed between the at least one metal interconnect and the first rate.

29. The stacked AW filter package of clause 27 or clause 28, wherein theinsulator is disposed between the at least one metal interconnect andthe first surface of the first substrate.

30. The stacked AW filter package of any of clauses 27-29, wherein theinsulator is disposed between the at least one metal interconnect andthe side wall surface of the second substrate.

31. The stacked AW filter package of any of any of clauses 27-30,further comprising a via extending through the second substrate from thecontact surface to the first surface of the first substrate.

32. The stacked AW filter package of clause 31, further comprising acontact on the contact surface, wherein:

-   -   the contact pad is configured to conduct electrical signals; and    -   the via is configured to electrically couple the first AW        circuit to the contact pad.

33. The stacked AW filter package of any of clauses 27-32, wherein:

-   -   a thickness of the third substrate, in a first direction        orthogonal to a second surface, is in a range of 60 to 130        micrometers (μm);    -   a thickness of the first substrate in the first direction is in        a range of 30 to 70 μm; and    -   a thickness of the second substrate in the first direction is in        a range of 30 to 70 μm.

34. The stacked AW filter package of any of clauses 27-33, wherein:

-   -   the thickness of the first substrate is less than 85 μm;    -   the thickness of the third substrate is less than 55 μm; and    -   the thickness of the second substrate is less than 55 μm.

35. A method of forming a stacked acoustic wave filter (AW filter)package, comprising:

-   -   forming a first substrate comprising a first surface and a side        wall surface;    -   forming a first AW filter circuit on the first surface of the        first substrate;    -   forming a first frame on the first surface of the first        substrate;    -   forming a second substrate comprising a contact surface and a        side wall surface;    -   disposing the second substrate on the first frame to form a        first cavity between the first AW filter circuit and the second        substrate;    -   forming a third substrate comprising a second AW filter circuit        on a second surface of the third substrate;    -   forming a second frame on the second surface of the third        substrate;    -   disposing the first substrate on the second frame to form a        second cavity between the second AW filter circuit and the first        substrate;    -   forming an insulator on the side wall surface of the first        substrate; and    -   forming a metallization layer comprising at least one metal        interconnect coupled to the contact surface of the second        substrate and the second surface of the third substrate, the at        least one metal interconnect disposed on the insulator on the        side wall surface of the first substrate.

What is claimed is:
 1. A stacked acoustic wave (AW) filter package,comprising: a first substrate comprising a first surface; an AW filtercircuit on the first surface of the first substrate; a frame disposed onthe first surface of the first substrate; a second substrate comprisinga contact surface and a side wall surface, the second substrate disposedon the frame to form a cavity between the AW filter circuit and thesecond substrate; and a metallization layer comprising at least onemetal interconnect coupled to the contact surface of the secondsubstrate and the first surface of the first substrate, the at least onemetal interconnect disposed on the side wall surface of the secondsubstrate.
 2. The stacked AW filter package of claim 1, furthercomprising a contact pad coupled to the contact surface; the at leastone metal interconnect configured to redistribute signals from thecontact pad to the first surface of the first substrate.
 3. The stackedAW filter package of claim 1, wherein: the frame is disposed between thesecond substrate and the first surface of the first substrate, extendingfrom the side wall surface of the second substrate in a directionorthogonal to the side wall surface of the second substrate on a firstside of the side wall surface of the second substrate; and the firstsurface of the first substrate includes a shoulder area on a second sideof the side wall surface of the second substrate in the directionorthogonal to the side wall surface of the second substrate.
 4. Thestacked AW filter package of claim 3, wherein: the at least one metalinterconnect is disposed on the shoulder area of the first surface ofthe first substrate.
 5. The stacked AW filter package of claim 4,further comprising a contact pad on the contact surface, the contact padconfigured to couple to an external circuit, wherein the at least onemetal interconnect is electrically coupled to the contact pad.
 6. Thestacked AW filter package of claim 4, further comprising a surfaceinterconnect on the first surface of the first substrate extending frominside the cavity to the shoulder area, the surface interconnectelectrically coupled to the AW filter circuit, and the at least onemetal interconnect of the metallization layer on the shoulder area. 7.The stacked AW filter package of claim 6, wherein the at least one metalinterconnect of the metallization layer is disposed on a side surface ofthe frame between the second substrate and the first substrate.
 8. Thestacked AW filter package of claim 7, wherein: the frame extends in thedirection orthogonal to the side wall surface of the second substrateinto the shoulder area on the second side of the side wall surface ofthe second substrate; and the at least one metal interconnect of themetallization layer is disposed on a top surface of the frame.
 9. Thestacked AW filter package of claim 1, wherein the frame comprises afirst material, and the second substrate comprises a second materialdifferent than the first material.
 10. The stacked AW filter package ofclaim 9, wherein: the frame comprises a polymer material; the secondsubstrate comprises a glass; and the first substrate comprises asemiconductor material.
 11. The stacked AW filter package of claim 1,wherein: the frame further comprises a perimeter frame disposed along aperimeter of the second substrate; and the cavity is surrounded by eperimeter frame.
 12. The stacked AW filter package of claim 11, whereinthe frame further comprises a frame member extending into the cavity,orthogonal to at least a portion of the perimeter frame.
 13. The stackedAW filter package of claim 12, wherein the frame member comprises one ofa plurality of frame members of the frame.
 14. The stacked AW filterpackage of claim 12, the frame member further comprising a linear framemember comprising a first end coupled to the perimeter frame.
 15. Thestacked AW filter package of claim 14, the cavity comprising acontinuous cavity extending from a first cavity section on a first sideof the linear frame member and around a second end of the linear framemember to a second cavity section on a second side of the linear framemember.
 16. The stacked AW filter package of claim 15, where the AWfilter circuit on the first surface of the first substrate is a first AWfilter circuit; the first AW filter circuit is disposed in the firstcavity section on the first side of the linear frame member; and thestacked AW filter package further comprises another AW filter circuit onthe second side of the linear frame member.
 17. The stacked AW filterpackage of claim 1, wherein the cavity comprises a continuous circularregion having a diameter up to 400 micrometers (μm) from which the frameis excluded.
 18. The stacked AW filter package of claim 17, wherein thediameter of the continuous circular region is greater than 360 μm. 19.The stacked AW filter package of claim 5, the stacked AW filter packagefurther comprising: a third substrate comprising a second AW filtercircuit on a second surface of the third substrate; and a second framedisposed on the second surface of the third substrate; wherein: thefirst substrate is disposed on the second frame to form a second cavitybetween the second AW filter circuit and the first substrate.
 20. Thestacked AW filter package of claim 19, wherein: the first substratefurther comprises a side wall surface orthogonal to the first surface ofthe first substrate; the second frame is disposed between the firstsubstrate and the second surface of the third substrate, extending fromthe side wall surface of the first substrate in a direction orthogonalto the side wall surface of the first substrate on a first side of theside wall surface of the first substrate; and the second surface of thethird substrate includes a lower shoulder area on a second side of theside wall surface of the first substrate in the direction orthogonal tothe first side wall surface of the first substrate.
 21. The stacked AWfilter package of claim 20, wherein: the at least one metal interconnectis disposed on: the side wall surface of the first substrate; and thelower shoulder area of the second surface of the third substrate. 22.The stacked AW filter package of claim 21, further comprising a surfaceinterconnect on the second surface of the third substrate extending frominside the second cavity to the lower shoulder area, the surfaceinterconnect electrically coupled to the second AW filter circuit, andthe at least one metal interconnect on the lower shoulder area.
 23. Thestacked AW filter package of claim 21, wherein the at least one metalinterconnect is disposed on a side surface of the second frame betweenthe first substrate and the third substrate.
 24. The stacked AW filterpackage of claim 23, wherein: the second frame extends in the directionorthogonal to the side wall surface of the first substrate onto thelower shoulder area on the second side of the side wall surface of thefirst substrate; and the at least one metal interconnect is disposed ona top surface of the second frame.
 25. A method of fabricating a stackedacoustic wave (AW) filter package, the method comprising: forming afirst substrate comprising a first surface; forming an AW filter circuiton the first surface of the first substrate; forming a frame on thefirst surface of the first substrate; forming a second substratecomprising a contact surface and a side wall surface; disposing thesecond substrate on the frame to form a cavity between the AW filtercircuit and the second substrate; and forming a metallization layercomprising at least one metal interconnect coupled to the contactsurface of the second substrate and the first surface of the firstsubstrate, the at least one metal interconnect disposed on the side wallsurface of the second substrate.
 26. The method of claim 25, furthercomprising: disposing the frame between the second substrate and thefirst surface of the first substrate, and extending from the side wallsurface of the second substrate in a direction orthogonal to the sidewall surface of the second substrate on a first side of the side wallsurface of the second substrate; and forming a shoulder area of thefirst surface of the first substrate on a second side of the side wallsurface of the second substrate in the direction orthogonal to the sidewail surface of the second substrate.
 27. A stacked acoustic wave (AW)filter package, comprising: a first substrate comprising a first surfaceand a side wall surface; a first AW filter circuit on the first surfaceof the first substrate; a first frame disposed on the first surface ofthe first substrate; a second substrate comprising a contact surface anda side wall surface, the second substrate disposed on the first frame toform a first cavity between the first AW filter circuit and the secondsubstrate; a third substrate comprising a second AW filter circuit on asecond surface of the third substrate; a second frame disposed on thesecond surface of the third substrate; the first substrate disposed onthe second frame to form a second cavity between the second AW filtercircuit and the first substrate; a metallization layer comprising atleast one metal interconnect coupled to the contact surface of thesecond substrate and the second surface of the third substrate, the atleast one metal interconnect disposed on the side wall surface of thefirst substrate; and an insulator disposed on the side wall surface ofthe first substrate between the side wall surface of the first substrateand the at least one metal interconnect.
 28. The stacked AW filterpackage of claim 27, wherein the insulator is disposed between the atleast one metal interconnect and the first frame.
 29. The stacked AWfilter package of claim 27, wherein the insulator is disposed betweenthe at least one metal interconnect and the first surface of the firstsubstrate.
 30. The stacked AW filter package of claim 27, wherein theinsulator is disposed between the at least one metal interconnect andthe side wall surface of the second substrate.
 31. The stacked AW filterpackage of claim 28, further comprising a via extending through thesecond substrate from the contact surface to the first surface of thefirst substrate.
 32. The stacked AW filter package of claim 31, furthercomprising a contact pad on the contact surface, wherein: the contactpad is configured to conduct electrical signals; and the via isconfigured to electrically couple the first AW circuit to the contactpad.
 33. The stacked AW filter package of claim 28, wherein: a thicknessof the third substrate, in a first direction orthogonal to a secondsurface, is in a range of 60 to 130 micrometers (μm); a thickness of thefirst substrate in the first direction is in a range of 30 to 70 μm; anda thickness of the second substrate in the first direction is in a rangeof 30 to 70 μm.
 34. The stacked AW filter package of claim 33, wherein:the thickness of the first substrate is less than 85 μm; the thicknessof the third substrate is less than 55 μm; and the thickness of thesecond substrate is less than 55 μm.
 35. A method of forming a stackedacoustic wave filter (AW filter) package, comprising: forming a firstsubstrate comprising a first surface and a side wall surface; forming afirst AW filter circuit on the first surface of the first substrate;forming a first frame on the first surface of the first substrate;forming a second substrate comprising a contact surface and a side wallsurface; disposing the second substrate on the first frame to form afirst cavity between the first AW filter circuit and the secondsubstrate; forming a third substrate comprising a second AW filtercircuit on a second surface of the third substrate; forming a secondframe on the second surface of the third substrate; disposing the firstsubstrate on the second frame to form a second cavity between the secondAW filter circuit and the first substrate; forming an insulator on theside wall surface of the first substrate; and forming a metallizationlayer comprising at least one metal interconnect coupled to the contactsurface of the second substrate and the second surface of the thirdsubstrate, the at least one metal interconnect disposed on the insulatoron the side wall surface of the first substrate.